Initial reef building of the Devonian Elbingerode barrier reef complex, Harz Mts., Germany

The Elbingerode reef complex is a large Devonian reef system in the central Harz Mountains of Germany. It is well known for its massive, thick and fossil-rich limestones that formed an oceanic barrier reef system in the Rhenohercynian Basin of the Paleotethys Ocean. The initial reef building of this barrier reef system is less well known, but exposed in the form of small outcrops at the boundaries of underlying volcanic rocks and superposed reef limestone. Also, waste rock piles of ore mining have contributed to the knowledge of these deposits, especially to their fossil content. These limestones have been revisited and investigated with regard to sedimentology, mineralogy, and biostratigraphy. The initial reef building is reflected in the occurrence of biogenic packstones, grainstones, and wackestones deposited in close relationship to volcanic activity. The limestones are rich in crinoidal debris (as the main constituent particle), brachiopods, rugose and tabulate corals, stromatoporoids, bryozoa, trilobites, tentaculites, ostracodes, conodonts, goniatites, and holothurians. Clasts of volcanic rocks are common. The fine-grained matrix of the deposits contains 60-80% carbonate and considerable amounts of non-carbonate fines. Reef frameworks did not form, but the common occurrence of numerous organism groups underlines that a highly diverse fauna had developed in a stressed environment including volcanic activity, and likely elevated turbidity and reduced water transparency. The textures and fabrics encountered suggest deposition below the fair-weather wave base, i.e., in water depths of several meters to a few tens of meters, however, not in shallow, agitated water.